Enhancing therapeutic effectiveness of nitric oxide inhalation

ABSTRACT

Methods for reducing, partially preventing or completely preventing nitric oxide (NO) inhalation-related impairment of HPV in a mammal are disclosed. The methods include administering a therapeutically effective amount of NO by inhalation, and co-administering an effective amount of an anti-reactive oxygen species (anti-ROS) agent, e.g., N-acetylcysteine, or a leukotriene blocker. Methods for reducing, partially preventing or completely preventing loss of pulmonary vasodilatory responsiveness to NO inhalation in a mammal are also disclosed. The methods include administering a therapeutically effective amount of NO by inhalation, and co-administering an effective amount of an anti-ROS agent a therapeutically effective amount of a leukotriene blocker.

TECHNICAL FIELD

This invention relates to pulmonary physiology and cardiology.

BACKGROUND

Nitric oxide (NO) is a highly reactive free radical compound produced bymany cells of the body. It relaxes vascular smooth muscle by binding tothe heme moiety of cytosolic guanylate cyclase, activating guanylatecyclase and increasing intracellular levels of cyclic guanosine3′,5′-monophosphate (cGMP), leading to vasodilation.

When inhaled, NO gas acts as a selective vasodilator of human and animalpulmonary vessels. Consequently, NO inhalation is used to promotevasodilation in well-ventilated regions of the lung. In acuterespiratory distress syndrome (ARDS), impaired ventilation of lungtissue reduces oxygenation of arterial blood. Nitric oxide inhalationoften improves oxygenation in ARDS patients. It does so by dilatingblood vessels in well-ventilated portions of the lung, redistributingblood flow towards the well-ventilated regions and away frompoorly-ventilated regions, which receive little NO. However, in 30-40%of ARDS patients, NO inhalation fails to improve arterial oxygenation(Bigatello et al., 1994, Anesthesiology 80:761-770; Dellinger et al.,1998, Crit. Care Med. 26:15-23). It is difficult to predict whichpatients with ARDS will not respond to NO inhalation or which patientswill respond only transiently. However, it is known that up to 60% ofpatients with ARDS associated with sepsis do not respond to inhaled NO(Krafft et al., 1996, Chest 109:486-493).

Normal pulmonary vasculature constricts in response to alveolar hypoxia.In patients with lung injury such as ARDS, hypoxic pulmonaryvasoconstriction (HPV) raises the level of systemic arterial oxygenationby redistributing blood flow away from a poorly ventilated (hypoxic)lung or lung region toward a well-ventilated (normoxic) lung regions.Sepsis and endotoxemia impair HPV (Hutchinson et al., 1985, J. Appl.Physiol. 58:1463-1468) leading to a profound decrease in arterial oxygenconcentrations. Such a decreased level of systemic oxygenation can belife-threatening. Nitric oxide inhalation might be expected to improveoxygenation or arterial blood during sepsis, by increasing blood flow inwell-ventilated regions on the lung. In practice, however, NO inhalationduring sepsis is often ineffective, and sometimes is deleterious,because of NO inhalation-related reduction of HPV. See, e.g., Gerlach etaL., 1996, “Low levels of inhaled nitric oxide in acute lung injury,”pages 271-283 in Nitric Oxide and the Lung, (Zapol and Bloch, eds.),Marcel Dekker Inc, New York.

Endogenous NO is produced by nitric oxide synthases through conversionof L-arginine to L-citrulline in the presence of oxygen (Knowles et al.,1994, Biochemistry 298:249-258). Three different forms of nitric oxidesynthase (NOS) have been characterized. Neuronal NOS (NOS1) andendothelial NOS (NOS3) are constitutive enzymes. An inducible NOS knownas NOS2 capable of producing large amounts of NO is induced by endotoxin(also referred to as lipopolysaccharide or LPS) and cytokines (Knowleset al., supra). In spite of the demonstrated value of NO inhalationtherapy for various indications, impaired pulmonary vascular dilatoryresponsiveness to NO inhalation and NO-related loss of HPV remainsignificant problems in acute respiratory illness.

SUMMARY

The inventors have discovered that an increased pulmonary NO level isnecessary to to impair HPV during sepsis, and that such HPV impairmentcan be ameliorated by reactive oxygen species scavengers or leukotrieneblockers. Accordingly, the inventors have developed methods forpreserving the vasodilatory effect of NO inhalation to achieve improvedarterial blood oxygenation in patients with lung injury, whileameliorating HPV-reducing effects of NO inhalation. The inventors havediscovered that the impairment of HPV is not simply NO-mediatedvasodilation. The inventors also have discovered that an elevated levelof pulmonary NO plus other lipopolysaccharide-induced agents arenecessary to impair pulmonary vasodilatory responsiveness to NOinhalation in endotoxin-challenged mice. Accordingly, the inventors havedeveloped methods for preserving pulmonary vasodilator responsiveness toNO inhalation.

In one aspect, the invention features a method for reducing, partiallypreventing or completely preventing NO inhalation-related impairment ofHPV in a mammal. In one embodiment, the method includes administering tothe mammal a therapeutically effective amount of NO by inhalation, andco-administering an effective amount of an anti-reactive oxygen species(anti-ROS) agent. The anti-ROS agent can be, e.g., N-acetylcysteine,allopurinol, ascorbic acid (vitamin C), bilirubin, caffeic acid,catalase, PEG-catalase, ceruloplasm, copper diisopropylsalicylate,deferoxamine mesylate, dimethylurea, ebselen(2-phenyl-1,2-benzisoselenazol-3(2H)-one; Pz51), EUK-8, FeTMTPyP (5, 10,15, 20-tetrakis(N-methyl-4′-pyridyl)porphinato iron (III) chloride),FETPPS (5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III)chloride), glucocorticoids, glutathione, MnTBAP(Mn(III)tetrakis(4-benzoic acid)porphyrin chloride), MnTMPyP(Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride),selenomethionine, superoxide dismutase (SOD), polyethyleneglycol-conjugated-SOD (PEG-SOD), Taxifolin (dihydroquercetin;3,3′,4′,5,7-pentahydroxyflavone), and vitamin E. N-acetylcysteine is apreferred anti-ROS agent. In alternative embodiment, the method includesadministering a therapeutically effective amount of NO by inhalation,and co-administering an effective amount of a leukotriene blocker. Inother embodiments, two or more anti-ROS agents, or an anti-ROS agent anda leukotriene blocker are co-administered with NO inhalation.

In another aspect, the invention features methods for reducing,partially preventing or completely preventing loss of pulmonaryvasodilatory responsiveness to NO inhalation in a mammal. In oneembodiment, the method includes administering to the mammal atherapeutically effective amount of NO by inhalation, andco-administering an effective amount of an anti-ROS agent. Inalternative embodiment, the method includes administering atherapeutically effective amount of NO by inhalation, andco-administering an effective amount of a leukotriene blocker. In otherembodiments, two or more anti-ROS agents, or an anti-ROS agent and aleukotriene blocker are co-administered with NO inhalation.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by a person of ordinaryskill in the art to which the invention belongs. In case of conflict,the present application, including definitions, will control. Allpublications, patents, and other documents mentioned herein areincorporated by reference.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the invention, thepreferred methods and materials are described below. The materials,methods and examples are illustrative only and not intended to belimiting. Other features and advantages of the invention will beapparent from the detailed description and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a tracing from a representative experiment measuring pulmonaryartery pressure (PAP; equivalent to perfusion pressure) and left atrialpressure (LAP) in an isolated-perfused lung of an untreated wild-typemouse. The stable thromboxane A₂ analog U46619 was infused to increasePAP by 5 or 6 mmHg. Varying doses (0.4, 4.0, and 40 ppm) of NO gas wereadministered for 5 minutes each. After each dose, PAP was allowed toreturn to the pre-NO level.

FIG. 2A is a dose-response curve for NO inhalation inlipopolysaccharide-pretreated (closed circles) and untreated (opencircles) wild-type mice. The response to NO inhalation was impaired inlipopolysaccharide-pretreated wild-type mice, as compared to untreatedwild-type mice (*P<0.001). Data are expressed as mean±SE. ΔPAP=change inpulmonary artery pressure as percent of its U46619-induced increase.

FIG. 2B is a dose-response curve for NO inhalation inlipopolysaccharide-pretreated (closed squared) and untreated (opensquares) NOS2-deficient mice. Lipopolysaccharide-treated NOS2-deficientmice had a greater response to NO inhalation, as compared to untreatedNOS2-deficient mice (†P<0.05) and lipopolysaccharide-pretreatedwild-type mice (‡P<0.001). Data are expressed as mean±SE. ΔPAP=change inpulmonary artery pressure as percent of its U46619-induced increase.

FIG. 3 is a graph summarizing data on vasodilation by short term NOinhalation in isolated-perfused lungs from lipopolysaccharide-pretreated(wild-type/LPS) and untreated (wild-type/control) wild-type mice, and inisolated-perfused lungs from lipopolysaccharide-pretreated (ko/LPS) anduntreated (ko/control) NOS2-deficient mice previously exposed to 20 ppmNO for 16 hours in ambient air. After prolonged NO exposure,lipopolysaccharide-pretreated NOS2 deficient mice were less responsiveto short-term NO inhalation than were NOS2-deficient mice that did notreceive lipopolysaccharide (*P<0.05). Similarly, after prolonged NOexposure, lipopolysaccharide-pretreated wild-type mice were lessresponsive to short-term NO inhalation than were wild-type mice that didnot receive lipopolysaccharide (*P<0.05). Data are expressed as mean±SE.

FIG. 4 is a histogram summarizing data from experiments on the effectsof breathing 0, 0.2, 2.0 and 20 ppm NO for 16 hours afterlipopolysaccharide challenge on the subsequent vasodilation in responseto short-term inhalation of 0.4 ppm NO gas, in isolated-perfused lungsobtained from NOS2-deficient mice. Exposure to 2 and 20 ppm NO gasdecreased the pulmonary vasodilatory response to NO. Data are expressedas mean±SE. *P<0.05; **P<0.001 versus 0 ppm NO exposure for 16 hours.

FIG. 5 is a graph summarizing data from experiments on the pulmonaryvasodilator response to NO inhalation in lipopolysaccharide-challenged(closed circles) and control mice (open circles), and inlipopolysaccharide-challenged mice treated with N-acetylcysteine (150mg/kg i.p.) simultaneously with lipopolysaccharide and repeated 3.5hours later (closed triangles). The response to NO inhalation wasattenuated in lipopolysaccharide-treated mice as compared to controlmice (*P<0.001). Two doses of N-acetylcysteine (150 mg/kg) completelyprotected against polysaccharide-induced attenuation of vasoreactivityto NO inhalation. %vasodilation is change in pulmonary artery pressureas percent of U46619-induced increase. Data are expressed as mean±SE.

FIG. 6 is a graph summarizing data from experiments on the pulmonaryvasodilator response to NO inhalation in lipopolysaccharide(LPS)-challenged mice that were treated with a simultaneousintraperitoneal injection of N-acetylcysteine or saline, and thatbreathed either room air or room air plus 20 ppm NO gas for 16 hours.The protective effect of N-acetyl-cycteine 150 mg/kg on the pulmonaryvasodilator response to NO in lipopolysaccharide-challenged mice waspreserved during prolonged NO inhalation. (*P<0.05 vs. LPS+saline inboth groups).

FIG. 7 is a histogram summarizing data from experiments on change infractional blood flow to the left lung (QLPA/QPA) 5 minutes after leftmainstem bronchus occlusion (LMBO) in wild-type mice (+/+) andNOS2-deficient mice (−/−) treated with saline (control, open bars; n=7),endotoxin (endotoxin, closed bars; n=6), or endotoxin with 5 mg/kg L-NILintraperitoneally (endotoxin with L-NIL (a selective NOS2 inhibitor),striped bar; n=5) administered 3 hours after the endotoxin challenge.(*P<0.05, endotoxin versus control; P<0.01, wild-type versusNOS2-deficient; #P<0.01 endotoxin+L-NIL versus endotoxin alone).Measurements were obtained following 1 hour after discontinuation ofbreathing air or 40 ppm NO in air for 22 h (§P<0.05 NO versus withoutNO). Endotoxin challenge caused a marked reduction of pulmonary bloodflow redistribution after LMBO in wild-type, but not in NOS2-deficientmice. After prolonged inhalation of 40 ppm NO, endotoxin-treatedNOS2-deficient mice, measured 1 hour after discontinuation of NOinhalation, showed the same loss of HPV as endotoxin-treated wild-typemice. Saline-treated NOS2-deficient mice and wild-type mice breathing 40ppm NO for 22 hours retained their ability to redistribute pulmonaryblood flow after LMBO, when measured 1 hour after discontinuing NOinhalation.

FIG. 8 is a histogram summarizing results from experiments measuring thechange in incremental left pulmonary vascular resistance, ΔiLPV, inresponse to LMBO—a measure of hypoxic pulmonary vasoconstriction (HPV).HPV was impaired in wild-type mice challenged with endotoxin (ETX;#P<0.05 versus saline-challenged mice). HPV was preserved inendotoxin-challenged mice treated with 500 mg/kg (‡<0.05 versusuntreated endotoxin-challenged mice), but not 150 mg/kg (*P<0.05 versussaline-challenged mice), N-acetylcysteine (NAC; intraperitonealadministration of simultaneously with endotoxin). HPV was completelypreserved in endotoxin-challenged mice treated with EUK-8, a scavengerof superoxide, hydrogen peroxide and peroxynitrite (‡P<0.05 versusuntreated endotoxin-challenged mice).

FIGS. 9A-9C are representative tracings of pulmonary and systemichemodynamic measurements before and during LMBO with and withouttransient left pulmonary artery (LPA) occlusion. Effects of unilateralalveolar hypoxia induced by LMBO on central hemodynamics before (a) andduring LMBO (b and c) are portrayed. Total alveolar collapse occurredabout 1 minute after LMBO. Continuous recordings of mean flow throughthe right pulmonary artery (QRPA), mean pulmonary artery pressure (PPA),mean systemic arterial pressure (PSA), and mean airway pressure (PALV)in a saline-treated wild-type mouse at baseline and after LMBO. Toassess blood flow distribution between the right and left pulmonaryarteries, the left pulmonary artery was transiently occluded, at whichpoint QRPA=QPA (see a and c). The difference of QPA−QRPA equals QLPA.Measurements were taken at baseline and 5 minutes after LMBO. Arrowsindicate occlusion (90 seconds) and release of the left pulmonaryartery.

FIG. 10A is a graph showing correlation of percent pulmonary blood flowto the left or right lung assessed by intravenous injection offluorescent microspheres (15 μm dia.) and by simultaneous measurement ofQRPA with an ultrasonic flow probe. Values are expressed as thefractional flow to the right or left lung before and after LMBO(saline-treated wild-type mice; n=4). Note the close agreement betweenthe 2 methods (r2=0.967).

FIG. 10B is a graph showing results of experiments on the left lungpulmonary flow-pressure relationship before (baseline) and after 5minutes of LMBO in saline-treated wild-type mice (n=6). Left pulmonaryartery flow (QLPA) was measured by an ultrasonic flow probe, and theslopes were generated by reducing QPA with a transient occlusion of theinferior vena cava (P<0.05, slope differs versus baseline).

FIG. 10C is a graph illustrating changes in total left lung pulmonaryvascular resistance (TLPVR) during re-expansion of the collapsed leftlung in saline-treated wild-type mice (n=3). Values are expressed as alinear regression of all data points with the respective 95% confidenceintervals.

FIG. 11 is a graph showing effects of regional hypoxia induced by LMBOon the systemic arterial partial pressure of oxygen (PaO₂) inendotoxin-treated wild-type mice (thick line) and endotoxin-treatedNOS2-deficient mice (narrow line). Endotoxin was administered 22 hoursbefore study by an intraperitoneal injection of 10 mg/kg E. coliendotoxin. Continuous recordings of PaO₂ were obtained with a Clark-typeoxygen electrode located in the aortic arch. Data are the mean ofindependent experiments with wild-type mice (n=5) and NOS2-deficientmice (n=3).

FIG. 12 is a table of data from hemodynamic measurements. Hemodynamicmeasurements were before LMBO (baseline) and 5 minutes after left lunghypoxia (LMBO) in wild-type mice (NOS2 +/+) and NOS2-deficient mice(NOS2 −/−) challenged with saline (control) or endotoxin (endotoxin) 22hours before hemodynamic experiments, and with and without inhalation of40 ppm NO in air for 22 hours (as measured 1 hour after discontinuationof NO inhalation). HR=heart rate (min⁻¹), PSA=mean systemic arterialpressure (mmHg), P_(PA)=mean pulmonary artery pressure (mmHg), QPA=flowthrough right pulmonary artery during left pulmonary artery occlusion(μl×min⁻¹×g⁻¹bw), Q_(RPA)=flow through right pulmonary artery(μl×min⁻¹×g⁻¹bw), Q_(LPA)=flow through left pulmonary artery(μl×min⁻¹g⁻¹bw), Q_(LPA)/Q_(PA)=ratio of flow through left pulmonaryartery to flow through right pulmonary artery during transient leftpulmonary artery occlusion. All values at baseline before LMBO werecompared between groups by ANOVA. The effect of LMBO on each parameterwas analyzed in each group by ANOVA with a post hoc comparison(^(A)P<0.05, ^(B)P<0.01, ^(C)P<0.001 versus baseline).

FIG. 13 is a histogram summarizing data from experiments on theLMBO-induced increase in left lung pulmonary vascular resistance (leftPVR) in saline-challenged wild-type mice (n=7), saline-challenged5-LO-deficient (n=7) mice, endotoxin-challenged wild-type mice (n=8),endotoxin-challenged 5LO-deficient (n=9) mice, endotoxin-challengedwild-type mice treated with the 5-LO-activating protein inhibitor, MK886(n=8), and endotoxin-challenged wild-type mice treated with acysLT₁-receptor antagonist, MK571 (n=7). *P<0.01 vs. saline-challengedwild-type mice; #P<0.01 vs. endotoxin-challenged wild-type mice.

DETAILED DESCRIPTION

NO Inhalation

Methods for safe and effective administration of NO by inhalation arewell known in the art. See, e.g., Zapol, U.S. Pat. No. 5,570,683; Zapolet al., U.S. Pat. No. 5,904,938; Frostell et al., 1991, Circulation83:2038-2047. NO for inhalation is available commercially (INOmax™, INOTherapeutics, Inc., Clinton, N.J.). In the present invention, NOinhalation preferably is in accordance with established medicalpractice.

A suitable starting dosage for NO administered by inhalation is 20 ppm.See, e.g., INOmax™ package insert (www.inotherapeutics.com). However,dosage can vary, e.g., from 0.1 ppm to 100 ppm, depending on the age andcondition of the patient, the disease or disorder being treated, andother factors that the treating physician may deem relevant. Preferably,the lowest effective dose is inhaled. To arrive at the lowest effectivedosage empirically, administration can be commenced at 20 ppm and thendecreased gradually until vasodilator efficacy is lost. Where 20 ppm isdeemed an insufficient inhaled dose, NO dosage may be increasedgradually until vasodilator effectiveness is observed. Such adjustmentof dosage is routine for those of skill in the art. An advantage of thepresent invention is that in many cases it enables achievement of adesired therapeutic outcome at an NO dosage lower than that required ifNO were administered alone. In addition, it may allow for an inhaled NOresponse where none would occur otherwise, e.g., with septic lunginjury, or it may allow preservation of the response despite theprogress of acute lung injury.

Anti-ROS Agent

Reactive oxygen species (ROS) include the superoxide radical (O₂•),hydrogen peroxide (H₂O₂), and the hydroxyl radical (OH•). As usedherein, “anti-ROS agent” means a compound that: (1) inhibits productionof reactive oxygen species; or (2) scavenges, i.e., rapidly reacts with,reactive oxygen species, once produced. Numerous anti-ROS agents usefulin the present invention are known. Examples of anti-ROS agents include:N-acetylcysteine (Mucosil™), allopurinol, ascorbic acid (vitamin C),bilirubin, caffeic acid, catalase, PEG-catalase, catechin, ceruloplasm,copper diisopropylsalicylate, deferoxamine mesylate, dimethylurea,ebselen, EUK-8, FeTMTPyP, FETPPS, glucocorticoids, glutathione, MnTBAP,MnTMPyP, selenomethionine, superoxide dismutase, PEG-superoxidedismutase, Taxifolin, and vitamin E. In some embodiments of theinvention, two or more anti-ROS agents are employed in combination. Apreferred anti-ROS agents is N-acetylcysteine (MUCOSIL™, Dey, Napa,Calif.), which is commercially available in sterile solution (10% or20%) suitable for inhalation as an aerosol mist, e.g., using aconventional nebulizer.

Some anti-ROS agents also scavenge peroxynitrite, a toxic reactivenitrogen species produced by the reaction of NO with superoxide.Scavenging reactive nitrogen species may reduce, partially prevent orcompletely prevent NO inhalation-related impairment of HPV and loss ofpulmonary vasodilatory responsiveness to NO inhalation.

Dosage and route of administration of the anti-ROS agent(s) will dependon the particular agent(s) employed. Safe and effective dosages androutes of administration for the various anti-ROS agents are known inthe art. See, e.g., Physician's Desk Reference (PDR®), ClinicalPharmacology 2000, Gold Standard Multimedia(http://cp.gsm.com/fromcpo.asp), or vendor's package inserts.

A preferred anti-ROS agent is N-acetylcysteine, available commerciallyas MUCOMYST™, MUCOSIL-10™, and MUCOSIL-20™. Suitable routes ofadministration for N-acetylcysteine include oral, rectal, nebulizedaerosol, and intravenous. Ultrasonic or conventional nebulizers may beused to administer N-acetylcysteine. (Because N-acetyl-cysteine reactswith certain materials, e.g., iron, copper, and rubber, any part of thenebulizer equipment that comes in contact with N-acetylcysteine shouldbe made of plastic or glass.) Exemplary dosage regimens forN-acetylcysteine (MUCOSIL™) include, but are not limited to, thefollowing:

20-hour IV regimen: 150 mg/kg IV (diluted in 200 ml of D5W) over 15minutes, followed by 50 mg/kg IV (diluted in 500 ml of D5W) over 4hours, then 100 mg/kg IV (diluted in 1000 ml of D5W) over 16 hours.48-hour IV regimen: 140 mg/kg IV (diluted in 1:5 in D5W) over 1 hour,followed four hours after initiation of the loading dose by the first of12 doses of 70 mg/kg IV (diluted 1:5 in D5W) every 4 hours for a totaldose of 980 mg/kg. Each dose of the 48 hour regimen is given IV over 1hour.

Nebulization using face mask, mouth piece or tracheostomy: Adults andadolescents: 5-10 ml of 20% solution, or 10-20 ml of the 10% solutionevery 6-8 hours. Children: 3-5 ml of 20% solution, or 6-10 ml of the 10%solution every 6-8 hours. Infants: 1-2 ml of 20% solution, or 2-4 ml ofthe 10% solution every 6-8 hours.

Nebulization using tent or croupette: Adults and children: A sufficientvolume of 10% or 20% solution to provide a heavy mist, up to 300 ml maybe required.

Oral or rectal dosage for children: 5-30 ml of the 10% solution given3-6 times per day, e.g., 10 ml four times per day.

Preferably, administration of the anti-ROS agent is commencedconcurrently with NO inhalation initiation. Duration of anti-ROS agentadministration will depend on the agent employed and duration of the NOinhalation.

Leukotriene Blocker

Leukotrienes are a class of biologically active compounds that occurnaturally in leukocytes. Leukotrienes produce allergic and inflammatoryreactions similar to those of histamine. Arachidonic acid is convertedto leukotriene A4 by the action of 5-lipoxygenase (5LO) and the5LO-activating protein (FLAP). Leukotriene A4 is rapidly converted toleukotriene B4 (LTB4) and to leukotriene C4 (LTC4). LTC4, in turn, isconverted to leukotrienes D4 (LTD4) and E4 (LTE4). LTC4, LTD4 and LTE4,also referred to as cysteinyl leukotrienes, interact with CysLT1 andCysLT2 receptors. As used herein, “leukotriene blocker” means a compoundthat: (1) inhibits a step in the leukotriene biosynthetic pathway; or(2) inhibits leukotriene receptor activation. Example of leukotrieneblockers include: montelukast (SINGULAIR®; Merck; selective and orallyactive leukotriene receptor antagonist), zafirlukast (ACCOLATE®;AstraZeneca; selective peptide leukotriene receptor antagonist),zileuton (ZYFLO®; Abbott; orally active inhibitor of 5LO), prankulast,MK-571, MK-591, MK-886, BAY×1005, Cinalukast, Pobilukast edamine, MK-679and ZD2138. In some embodiments of the invention, two or moreleukotriene blockers are employed in combination. Preferred leukotrieneblockers are montelukast (SINGULAIR®), a selective and orally activeleukotriene receptor antagonist; zafirlukast (ACCOLATE®), a selectiveand competitive receptor antagonist of leukotriene D₄ (LTD₄) andleukotriene E₄ (LTD₄); and zileuton (ZYFLO®), an orally active inhibitorof 5LO.

Dosage and route of administration of the leukotriene blocker(s) willdepend on the particular agent(s) employed. Safe and effective dosagesand routes of administration for the various leukotriene blockers areknown in the art. See, e.g., Physician's Desk Reference (PDR®) orvendor's package inserts. For example, the preferred dosage ofzafirlukast (ACCOLATE®) in adult humans is 20 mg, twice daily, takenorally in tablet form. In another example, the preferred dosage ofmontelukast (SINGULAIR®) in adult humans is 10 mg, once daily, takenorally in tablet form.

Preferably, administration of the leukotriene blocker is commencedconcurrently with the initiation of NO inhalation. Duration ofleukotriene blocker administration will depend on the agent employed andthe duration of the NO inhalation.

Pulmonary Injury

While the invention can be utilized advantageously during NO inhalationtherapy in general, it is particularly useful for improving oxygenationin patients with acute pulmonary injury, including acute respiratorydistress syndrome (ARDS). Examples of acute pulmonary injury include:diffuse pulmonary infection (e.g., viral, bacterial, fungal); aspiration(e.g., gastric contents, water in cases of near drowning, meconium inneonates); inhalation of toxins and irritants (e.g., chlorine gas, NO₂,smoke, ozone, high concentrations of oxygen); narcotic overdosepulmonary edema (e.g., heroin, methodone, morphine, dextropropoxyphene);non-narcotic drug effects (e.g., nitrofurantoin); immunologic responseto host antigens (e.g., Goodpasture's syndrome, systemic lupuserythematosis); effects of nonthoracic trauma with hypotension (“lungshock”) in association with systemic reaction to processes initiatedoutside the lung (e.g., gram-negative septicemia, hemorrhagicpancreatitis, amniotic fluid embolism, fat embolism); and post-traumaticlung injury including lung contusion, lung transplantation,cardiopulmonary bypass lung injury, and postpneumonectomy pulmonaryedema.

Impaired HPV

The methods of the invention are useful for reducing, partiallypreventing or completely preventing NO inhalation-related impairment inHPV. Signs of an existing impairment in HPV include low bloodoxygenation (hypoxemia), which can be indicated by blue color ofpatient, reduced levels of oxymetric saturation, change in mentalstatus, neurologic dysfunction, dyspnea, tachycardia and hypotension.Symptoms of an existing impairment in HPV include shortness of breathand chest pain. Diagnosis of impairment or reduction in HPV is withinordinary skill in the art.

Patients at risk for development of impairment or reduction of HPVinclude patients with sepsis and patients with a potential lunginflammation. Lung inflammation can arise from conditions such aspneumonia or acute respiratory distress syndrome.

Impaired Responsiveness to NO Inhalation

The methods of the invention are useful for reducing, partiallypreventing or completely preventing loss of pulmonary vasodilatoryresponsiveness to NO inhalation. Loss of pulmonary vasodilatoryresponsiveness to NO means an inability of NO to increase oxygenation orto decrease pulmonary arterial pressure (PAP). Signs of inability todecrease PAP include reduced cardiac output and right heart failure,presenting as shock, edema and anasarca.

Patients at risk for loss of pulmonary vasodilatory responsiveness to NOinhalation include patients with sepsis and patients with a potentiallung inflammation. Lung inflammation can arise from conditions such aspneumonia or acute respiratory distress syndrome.

Experimental Information EXAMPLE 1 Anti-ROS Agents and Impairment ofPulmonary Vascular Responsiveness to NO

Experimental evidence was obtained demonstrating that scavengers ofreactive oxygen and reactive nitrogen species prevent the impairment ofpulmonary vascular responsiveness to NO inhalation byendotoxin-challenged mice. These experiments were performed by usingNOS2-deficient mice, in which prolonged NO inhalation together with anendotoxin-induced factor(s) other than NO impairs the ability of thepulmonary vasculature to vasodilate in response to subsequent NOinhalation. Responsiveness to NO inhalation was evaluated inisolated-perfused mouse lungs preconstricted with U46619. Wild-type micetreated with endotoxin 16 hours before isolation of lungs displayedimpaired responsiveness to NO inhalation (FIG. 2A). NOS2-deficient micetreated with endotoxin displayed nonimpaired responsiveness to NOinhalation (FIG. 2B). Wild-type mice exposed to 20 ppm NO for 16 hoursbefore isolation of lungs displayed nonimpaired responsiveness to NOinhalation. NOS2 deficient mice treated with endotoxin and exposed to 20ppm NO for 16 hours displayed impaired responsiveness to NO inhalation(FIG. 3). NOS2-deficient control mice receiving saline instead ofendotoxin and exposed to 20 ppm NO for 16 hours displayed nonimpairedresponsiveness to NO inhalation. In wild-type mice treated withendotoxin, scavengers of reactive oxygen and nitrogen species, includingN-acetyl cysteine (FIG. 5), dimethylurea, EUK8, and catalase preventedimpairment of responsiveness to NO inhalation. N-acetyl-cysteineprevented the impairment of pulmonary vascular responsiveness to NOinhalation in endotoxin-challenged wild-type mice despite prolonged NOinhalation (FIG. 6).

The experimental results shown in FIG. 5 demonstrated thatresponsiveness to NO inhalation was preserved in endotoxin-challengedwild-type mice treated with N-acetylcysteine. The experimental resultsshown in FIG. 6 indicated that the mechanism responsible for theprotective effect of N-acetylcysteine was not simply attributable tosuppression of endotoxin-induced pulmonary NOS2 expression.

Methods and Materials

These investigations were approved by the Subcommittee for ResearchAnimal Care of the Massachusetts General hospital. A total of 78 adultmale mice weighing 20-35 g were studied, as listed in table 1 andoutlined herein. NOS2-deficient mice (MacMicking et al., 1995, Cell81:641-650) were provided by Dr. Carl Nathan. Mice of the samebackground (F1-generation of the parental strains SV129 and C57 Black/6)were used as wild-type mice (Hickey et al., 1997, FASEB J. 11:955-964).

Isolated, Perfused, and Ventilated Mouse Lung Model Mice were killed byintraperitoneal injection of pentobarbital sodium (200 mg/kg bodyweight) and placed in a 37° C. water-jacketed chamber (Isolated PerfusedLung Size 1 Type 839; Hugo-Sachs Elektronik, March-Hugstetten, Germany).The trachea was isolated and intubated, and the lungs were ventilatedwith 21% O₂, 6% CO₂ and 73% N₂ using a volume-controlled ventilator(model 687; Harvard Apparatus, South Natick, Mass.) at a ventilatoryrate of 85 breaths/min and 2 cm H₂O end-expiratory pressure. The tidalvolume was adjusted to provide a peak inspiratory pressure of 10 cm H₂Othroughout each study. The lungs were exposed via a midline sternotomy,and a ligataure was placaed around the aorticopulmonary outflow tract.After injection of 10 IU heparin into the right ventricle, the pulmonaryartery was cannulated with a stainless steel cannula (1 mm ID) via theright ventricle. The pulmonary venous effluent was drained via astainless steel cannula (1 mm ID) placed through the apex of the leftventricle across the mitral valve and into the left atrium. Left atrialpressure was maintained at 2 mmHg. Lungs were perfused at a constantflow (50 ml. kg body weight⁻¹. min⁻¹; Ismatec Reglo-Analogue rollerpump; Laboratoriumstechnik GmbH, Wertheim-Mondfeld, Germany) with anon-recirculating system at 37° C. The perfusate used was Hanks'Balanced Salt Solution (GibcoBRL, Grand Island, N.Y.) containing 1.26 mMCaCl₂, 5.33 mM KC1, 0.44 mM KH₂PO₄, 0.50 mM MgCl₂, 0.41 mM MgSO₄, 138.0mM NaCl, 4.0 mM NaHCO₃, 0.3 mM Na₂HPO₄, and 5.6 mM glucose. Bovine serumalbumin, 5%, and dextran, 5% (both from Sigma Chemical Co., St. Louis,Mo.), were added to the perfusate to prevent pulmonary edema, in theisolated, perfused, and ventilated rat lung, essentially as described inHolzmann et al., 1996, Am. J. Physiol. 271:L981-L986. Indomethacin, 30mM (Sigma Chemical Co.), and 1 mM L-NAME (Sigma Chemical Co.) were addedto the perfusate to inhibit endogenous prostaglandin and NO synthesis,respectively. Sodium bicarbonate was added to adjust the perfusate pH to7.34-7.43.

Lungs were included in this study if they had a homogenous whiteappearance without signs of hemostasis or atelectasis and showed astable perfusion pressure less than 10 mmHg during the second 5 min ofan initial 10-min baseline perfusion period. Using these two criteria,approximately 15% of lung preparations from each group were discardedbefore study.

Pulmonary artery pressure (PAP) and left atrial pressure were measuredvia saline-filled membrane pressure transducers (Argon, Athens, Tex.)connected to a side port of the inflow and outflow cannulae,respectively. Airway pressure (Paw) was measured using a differentialpressure transducer (model MP-45-32-871; Validyne Engineering Corp.,Northridge, Calif.) connected to the inspiratory limb just before the Ypiece. Pressure transducers were connected to a biomedical amplifier(Hewlett Packard 7754B, Andover, Mass.), and data were recorded at 150Hz on a personal computer using an analog-to-digital interface with adata acquisition system (DI-220; Dataq Instruments, Akron, Ohio). Thesystem was calibrated before each experiment.

For NO inhalation, NO gas (800 or 80 ppm NO in nitrogen, Airco, MurrayHill, N.J.) was blended (Oxygen Blender; Bird Corporation, Palm Springs,Calif.) with oxygen, carbon dioxide, and nitrogen to achieve a finalconcentration of 21% O₂, 6% CO₂, and the desired NO concentration. NOand higher oxidative states of NO (NO_(x); CLD 700 AL; Eco Physics,Dürnten, Switzerland), oxygen (Hudson Ventronics Ddivision, Temecula,Calif.), and carbon dioxide (Datex CO2 monitor; Puritan-BennettCorpration, Los Angeles, Calif.) concentrations were monitoredcontinuously.

Pulmonary Vascular Response to NO inhalation after LipopolysaccharideChallenge Wild-type mice and NOS2-deficient mice were injectedintraperitoneally with 50 mg/kg body weight Escherichia coli 0111:B4lipopolysaccharide (LPS; Difco Laboratories, Detroit, Mich.) dissolvedin saline 16 h before isolated lung perfusion. This time point waschosen based on previous studies in rats (Holzmann et al., 1996, Am. J.Physiol. 271:L981-L986). Untreated wild-type and NOS2-deficient miceserved as controls.

After an initial 10-min baseline perfusion period, pulmonaryvasoconstrictin was induced by continuous infusion of the thromboxane A₂analog U-46619 (Cayman Chemicals, Ann Arbor, Mich.). The infusion ratewas adjusted to provide a stable increase in PAP of 5 or 6 mmHg. Then, adose-response curve to inhaled NO was obtained by sequentiallyventilating the lungs with 0.4, 4, and 40 ppm NO for 5 min each. Aftereach period of NO ventilation, the PAP was allowed to return to thepre-NO elevated baseline. U-46619 infusion was readjusted if the PAP wasnot within a range of ±10% of the pre-NO value at 5 min afterdiscontinuation of NO inhalation. The vasodilator response to inhaled NO(APAP) was measured as the change in PAP produced by inhaled NO (PAPafter 5 min of NO inhalation minus PAP pre-NO) as a percentage of theincrease in PAP induced by U-46619 (PAP pre-NO minus PAP at initialbaseline).

Effect of NO Exposure on Pulmonary Vascular Response to Inhaled NO Fourgroups of mice breathed 20 ppm NO for 16 h. One group of wild-type miceand one group of NOS2-deficient mice were injected with 50 mg/kglipopolysaccharide intraperitoneally immediately before NO exposure.Additional wild-type and NOS2-deficient mice groups were exposed to NOinhalation without receiving lipopolysaccharide. After 16 h of NOexposure, the lungs were isolated and perfused as described previously.Pulmonary vasoconstriction was induced by infusion of U46619, and thevasodilator response to 0.4, 4, and 40 ppm NO was measured.

During ambient-pressure NO exposure, animals were maintained in 40-1acrylic chambers. NO and NO_(x) concentrations were controlled carefullyusing soda lime²² at a high fresh gas flow rate of NO (10,000 ppm NO innitrogen; Airco, Murry Hill, N.J.), air, and oxygen, as previouslydescribed (Steudel et al., 1998, 101:2468-2477).

Two additional groups of NOS2-deficient mice were treated withlipopolysaccharide (50 mg/kg intraperitoneal) and then exposed to 0.2and 2 ppm NO inhalation, respectively. Sixteen hours later, isolatedlung perfusion studies measuring the degree of pulmonary vasodilationproduced by 0.4, 4, and 40 ppm inhaled NO were performed.

Wet-to-Dry Lung Weight Ratio At the end of each experiment, both lungs,excluding hilar structures, were excised and weighed (wet weight).Thereafter, the lungs were dried in a microwave oven for 60 min, aspreviously described (Holzmann et al., supra), and then reweighed (dryweight). Wet-to-dry lung weight ratios were calculated by dividing thewet weight by the dry weight.

Statistical Analysis All data are expressed as the mean±standard error(SE). To compare groups, a two-way analysis of variance was performed.When significant differences were detected by analysis of variance, apost hoc least significant difference test for planned comparisons wasused (Statistica for Windows; StatSoft, Inc., Tulsa, Okla.). Statisticalsignificance was assumed at a P value<0.05.

Results

Infusion of U46619 caused a stable increase of the PAP at a constantperfusate flow, which was reversible after discontinuing U46619 at theend of the experiment. The dose of U46619 necessary to increase the PAPby 5 or 6 mmHg did not differ in lipopolysaccharide-pretreated anduntreated wild-type and NOS2-deficient mice.

Mice injected with intraperitoneal lipopolysaccharide had piloerection,diarrhea, and lethargy to a similar degree in both wild-type andNOS2-deficient mice. The mortality rate 16 h after lipopolysaccharideinjection was approximately 15% and did not differ between the two mousestrains.

Pulmonary Vascular Response to NO Inhalation Inhalation of NO decreasedthe PAP in a dose-dependent manner in all groups. FIG. 1 is a tracingfrom a representative experiment measuring pulmonary artery pressure(PAP; equivalent to perfusion pressure) and left atrial pressure (LAP)in an isolated-perfused lung of an untreated wild-type mouse. The stablethromboxane A₂ analog U46619 was infused to increase PAP by 5 or 6 mmHg.Lungs were ventilated with varying concentrations of NO gas (0.4, 4.0,and 40 ppm) for 5 minutes each. After ventilation with NO wasdiscontinued, PAP was allowed to return to the pre-NO level. Theseresults demonstrate that, in isolated-perfused lungs of a mouse, it isfeasible to measure pulmonary artery pressure, to induce stablepulmonary vasoconstriction, and to reduce pulmonary vasoconstriction byventilation with low concentrations of NO gas.

In the isolated-perfused lungs of wild-type mice that underwentlipopolysaccharide challenge, PAP decreased 79% and 45% less in responseto 0.4 and 4 ppm inhaled NO, respectively, compared with untreatedanimals (P<0.001; FIG. 2A). The pulmonary vasodilator response to 40 ppmNO did not differ between these groups. Response to inhaled NO inuntreated NOS2-deficient mice did not differ from that of untreatedwild-type mice. In contrast, lungs obtained fromlipopolysaccharide-challenged NOS2-deficient mice showed greatervasodilatation to inhaled NO than the lungs oflipopolysaccharide-treated wild-type mice (P<0.001 at each NO dose; FIG.2B). Moreover, NO-induced vasodilation was enhanced inlipopolysaccharide-treated NOS2-deficient mice, compared with untreatedNOS-2deficient or wild-type mice (P<0.05, respectively, at each NO dose;FIG. 2B).

Data presented in FIG. 2A shows that endotoxin-challenge impaired theability of wild-type mice to dilate their pulmonary vasculature inresponse to ventilation with 0.4 and 40 ppm NO (*P<0.001). Datapresented in FIG. 2B shows that endotoxin-challenge did not impair thepulmonary vasodilator response to inhaled NO. Rather, endotoxinaugmented the ability of the pulmonary vasculature of NOS2-deficientmice to dilate in response to ventilation with 0.4, 4, and 40 ppm NO(†P<0.05). The pulmonary vasodilator response to inhaled NO was greaterin endotoxin-challenged NOS2-deficient mice than in endotoxin-challengedwild-type mice (‡P<0.001).

Pulmonary Vascular Response to NO After NO Inhalation Exposure Toinvestigate the role of molecular NO in the development ofhyporesponsiveness to NO inhalation, we studiedlipopolysaccharide-treated and untreated NOS2-deficient and wild-typemice that breathed air supplemented with 20 ppm NO for 16 h. Previous NOinhalation exposure did not alter the responsiveness to subsequentlyinhaled NO in perfused lungs obtained from untreated wild-type orNOS2-deficient mice or in lipopolysaccharide-pretreated wild-type mice.In contrast, the pulmonary vasodilator response to NO inhalation wasdecreased in lipopolysaccharide-pretreated NOS2-deficient mice exposedto ambient NO for 16 h, compared with non-NO-exposedlipopolysaccharide-pretreated NOS2-deficient mice. In isolated-perfusedlungs from NOS2-deficient mice exposed to 20 mm ambient NO for 16 h, thesubsequent vasodilator responsiveness to NO inhalation was impairedafter pretreatment with lipopolysaccharide (vs. untreated controls) at0.4 (ΔPAP−24±4% vs. −42±4%; P<0.05) and 4 ppm NO (ΔPAP−39±5% vs. −58±4%;P<0.01), but not at 40 ppm NO (ΔPAP−55±3% vs. −62±5%; P=not significant;FIG. 3. Similar to animals without previous NO inhalation exposure,NO-induced vasodilation was reduced in lipopolysaccharide-pretreatedwild-type mice, compared to untreated wild-type mice that had breathed20 mm NO for 16 h before lung perfusion experiments (FIG. 3).

After prolonged NO exposure, endotoxin-challenged NOS2-deficient micewere less responsive to short-term NO inhalation than wereNOS2-deficient mice that did not receive lipopolysaccharide (*P<0.05).Similarly, after prolonged NO exposure, lipopolysaccharide-pretreatedwild-type mice were less responsive to short-term NO inhalation thanwere wild-type mice that did not receive lipopolysaccharide (*P<0.05).These observations demonstrate that prolonged breathing of 20 mm NO doesnot impair the pulmonary vasodilator response to subsequent ventilationwith NO in untreated wild-type or NOS2-deficient mice. In contrast,prolonged breathing of 20 mm NO markedly impaired the pulmonaryvasodilator response to subsequent ventilation with NO inendotoxin-challenged NOS2-deficient mice (compare with data presented inFIG. 2B).

To determine whether the inhalation of a lower level of NO for 16 hwould impair vasoreactivity to short-term NO inhalation during lungperfusion, lipopolysaccharide-treated NOS2-deficient mice were exposedto 0.2 and 2 ppm NO inhalation. Breathing 0.2 ppm NO for 16 h afterlipopolysaccharide administration did not cause subsequenthyporesponsiveness to short-term inhaled NO in NOS2-deficient mice.However, breathing 2 ppm NO for 16 h decreased the vasodilator responseto 0.4 ppm NO inhalation, compared with the response in control mice(P<0.05; FIG. 4).

Wet-to-Dry Lung Weight Ratios The absence of pulmonary edema wasconfirmed by unchanged wet-to-dry lung weight ratios after perfusion.There was no difference between lipopolysaccharide-pretreated wild-type(wet weight-dry weight: 4.3±0.2) and NOS2-deficient (4.8±0.1) mice, oruntreated wild-type (4.6±0.1) and untreated NOS2-deficient (4.6±0.1)mice. Exposure to NO inhalation for 16 h did not alter the wet-to-drylung weight ratios in lipopolysaccharide-pretreated wild-type (4.9±0.1)and NOS2-deficient (5.1±0.2) mice or in untreated wild-type (4.5±0.3)and untreated NOS2-deficient (4.8±0.1) mice, compared with unexposedmice. Wet-to-dry lung weight ratios did not correlate with thevasodilator response to inhaled NO.

Effect of N-Acetylcysteine We investigated whether scavenging ofreactive oxygen species with N-acetylcysteine (NAC) prevented theimpairment of the pulmonary vasodilatory response to NO inhalation inendotoxin-challenged mice. Wild-type mice were treated with endotoxin(E. coli 011:B4-LPS, 50 mg/kg i.p.) followed by administration of normalsaline or NAC (150 mg/kg i.p.) immediately, and 3.5 hours later (n=5).Additional endotoxin-challenged mice treated with NAC breathed 20 mm NOfor 16 hours.

Mouse lungs were isolated, perfused, and ventilated 16 hours afterendotoxin challenge. Lungs from mice treated with saline alone andbreathing room air served as controls (n=10). Pulmonary vasoconstrictionwas induced with U46619, and the vasodilator response to 0.4, 4.0 and 40ppm NO by inhalation was measured. Vasodilation in response to 0.4, 4.0and 40 ppm NO in endotoxin-challenged mice was 32±13%, 43±10%, and53±8%, respectively, compared to that in control mice (p<0.001 vs.control) (FIG.6). In contrast, the vasodilator response to NO inhalationin endotoxin-challenged mice treated with NAC did not differ from thatin control mice (75±14%, 103±15%, and 91±7%, respectively (p<0.001 vs.LPS) (FIG. 6). Responsiveness to NO inhalation was also preserved inendotoxin-challenged, NAC-treated mice exposed to 20 mm NO. Thisindicated that NAC did not preserve responsiveness to acute NOinhalation by preventing the endotoxin-induced increase in pulmonary NOlevels. These results demonstrated the effectiveness of NAC (a scavengerof reactive oxygen species) in preventing endotoxin-induced impairmentof responsiveness to NO inhalation.

EXAMPLE 2 HPV and Scavengers of Reactive Oxygen Species

Experimental evidence was obtained demonstrating that scavengers ofreactive oxygen species prevent the impairment of HPV inendotoxin-challenged mice. To investigate the role for NOS2 inendotoxin-induced impairment of HPV, we compared ability of toredistribute pulmonary blood flow after left mainstream bronchusocclusion (LMBO) in wild-type mice and in mice with a congenitaldeficiency of NOS2. For these experiments, we developed a murine LMBOmodel. This allowed us to evaluate the impact of endotoxin on HPV inintact mice.

The results shown in FIG. 7 demonstrated that LMBO caused aredistribution of pulmonary blood flow away from the hypoxic left lungas reflected in a negative change in the ratio of left lung blood flowto total lung blood flow (Q_(LPA)/Q_(PA) ratio). Endotoxin challengecaused a marked reduction of pulmonary blood flow redistribution afterLMBO in wild-type mice (*P<0.05, endotoxin versus control) but not inNOS2-deficient mice (P<0.01, versus wild-type mice). Earlyadministration of L-NIL prevented the reduction in LMBO-inducedpulmonary blood flow redistribution (#P<0.01 versus endotoxin-challengedmice not treated with L-NIL). After prolonged inhalation of 40 ppm NO,endotoxin-treated NOS2-deficient mice showed the same loss of HPV as didendotoxin-challenged wild-type mice (§P<0.05 NO versus without NO).Saline-challenged NOS2-deficient mice and wildtype mice breathing 40 ppmNO for 22 hours retained their ability to redistribute pulmonary bloodflow after LMBO, when measured 1 hour after discontinuing NO inhalation.These results show that increased pulmonary NO levels due toendotoxin-induced NOS2 expression or due to NO inhalation are requiredto impair HPV after challenge with endotoxin. However, prolongedexposure to increased pulmonary NO levels alone are insufficient toimpair HPV (as measured 1 hour after discontinuation of NO inhalation).

We performed experiments on the change in incremental left pulmonaryvascular resistance, ΔiLPV, in response to LMBO—a measure of HPV. HPVwas impaired in wild-type mice challenged with endotoxin (FIG. 8). HPVwas preserved in endotoxin-challenged mice treated with N-acetylcysteineat 500 mg/kg, but not 150 mg/kg (intraperitoneal administrationsimultaneously with endotoxin). HPV was completely preserved inendotoxin-challenged mice treated with EUK-8, a scavenger of bothsuperoxide, hydrogen peroxide, and peroxynitrite.

From the above experiments we found that NOS2 deficiency protected micefrom endotoxin-induced impairment of HPV. We further found thatscavengers of reactive oxygen species prevented impairment of HPV inendotoxin-challenged, wild-type mice (FIG. 8).

Six lines of evidence supported these conclusions: (1) in wild-type miceLMBO increased pulmonary vascular resistance (PVR) in the left lung, but22 hours after endotoxin challenge LMBO-induced left lungvasoconstriction was impaired; (2) in endotoxin-challengedNOS2-deficient mice not exposed to NO, LMBO-induced left lungvasoconstriction was unimpaired (FIG. 7); (3) in endotoxin-challengedNOS2-deficient mice exposed to 40 ppm NO for 22 hours, LMBO-induced leftlung vasoconstriction was impaired (FIG. 7); (4) prolonged NO inhalationalone did not impair HPV in mice, (FIG.); (5) N-acetylcysteine or EUK-8prevented impairment of HPV in endotoxin-challenged wild-type mice (FIG.8); and (6) HPV was not impaired in endotoxin-challenged wild-type micetreated with N-acetylcysteine and exposed to 20 ppm NO for 22 hours.

Methods and Materials

After institutional approval by the Massachusetts General HospitalSubcommittee on Research Animal Care, we studied SV129/B6F1 wild-typemice (F1-generation progeny of SV129 and C57 BL/6 mice) and SV129wild-type mice (The Jackson Laboratory, Bar Harbor, Me., USA), as wellas NOS2-deficient mice with a SV129 and C57BL/6 hybrid background(MacMicking et al., 1995, Cell 81:641-650)(provided by C. Nathan,Cornell University, New York, N.Y.). In supplemental studies,NOS2-deficient mice (18), backcrossed 10 generations onto a C57BL/6background (C57BL/6-Nos2tmlLau, N10-backcross generation; The JacksonLaboratory), and wild-type C57BL/6 were studied.

Experimental groups matched for animal age, body weight, and sex wereused. Male and female mice with an age range of 2-5 months,weighing18-30 g, were studied.

Group 1: controls. SV129/B6F1 wild-type mice (n=5), SV129 wild-type mice(n=7), and NOS2-deficient mice (n=7) received an intraperitonealinjection of 0.2 mL saline and were studied 22 hours later.

Group 2: endotoxin-treated. SV129/B6F1 wild-type mice (n =5), SV129wild-type mice (n=6), and NOS2-deficient mice (n=6)were studied 22 hoursafter a challenge with an intraperitoneal injection of 10 mg/kgEscherichia coli 011 B4 endotoxin dissolved in 0.2 mL saline.Additionally, C57BL/6 wild-type mice (n=7) and C57BL/6-Nos2tmlLau mice(n=5) were studied 22 hours after a challenge with an intraperitonealinjection of 10 mg/kg endotoxin dissolved in 0.2 mL saline.

Group 3: endotoxin-treated+L-NIL. SV129/B6F1 wild-type mice (n=5) wereinjected intraperitoneally with 10 mg/kg E. coli 011 B4 endotoxindissolved in 0.2 mL saline. Three hours after the endotoxin challenge,mice were treated with L-NIL 5 mg/kg intraperitoneally. Studies wereperformed 22 hours after the endotoxin challenge. In additionalSV129/B6F1 mice with (n=5) and without (n=4) a prior challenge ofendotoxin (22 hours earlier), the acute response to an intravenous bolusof 5 mg/kg L-NIL administered during LMBO, was studied. We chose a doseof 5 mg/kg intraperitoneal L-NIL because similar doses have been shownto effectively inhibit NOS2 activity in vivo in rodent models ofinflammation (Schwartz et al., 1997, J. Clin. Invest. 100:439-448).

Group 4: prolonged exposure to 4 or 40 ppm NO. Saline-treated SV129wild-type mice (n=5) and NOS2-deficient mice (n=5) breathed 40 ppm NO inair for 22 hours and were studied 1 hour after discontinuation of NOinhalation. SV129 wild-type mice (n=5) and NOS2-deficient mice (n=5)breathed 40 ppm NO in air for 22 hours after challenge with 10 mg/kgendotoxin intraperitoneally and were studied 1 hour afterdiscontinuation of NO inhalation. Additional NOS2-deficient mice (n=4)breathed 4 ppm of NO in air for 22 hours after challenge with 10 mg/kgendotoxin intraperitoneally and were studied 1 hour afterdiscontinuation of NO inhalation.

Group 5: continuous PaO₂ and PvO₂ measurements. PaO₂ was assessedcontinuously before and during LMBO in SV129/B6F1 wild-type mice (n =3)and NOS2-deficient mice (n=3) 22 hours after challenge with 10 mg/kgendotoxin intraperitoneally. PvO₂ was assessed continuously before andduring LMBO in SV129/B6F1 wild-type mice (n=4) and NOS2-deficient mice(n=4) 22 hours after challenge with 10 mg/kg endotoxinintraperitoneally. In saline-treated SV129 wild-type mice, PaO₂ (n=4)and PvO₂ (n=4) were studied before and during LMBO under controlconditions, without a prior challenge of endotoxin.

Group 6: pulmonary vascular response to increasing doses of intravenousangiotensin II. SV129/B6F1 wild-type mice treated with endotoxin (n=5)or with saline (n=3) were studied 22 hours after the challenge.

Experimental preparation. Mice were anesthetized by intraperitonealinjection of ketamine (0.1 mg/g body weight [bw]). Tracheostomy andarterial catheterization were performed as described previously (Steudelet al., 1997, Circ. Res. 81:34-41). A custom-made endotracheal tube (22GAngiocath; Becton Dickinson Healthcare Systems, Sandy, Utah, USA),combined with a 2 French Fogarty arterial embolization catheter (BaxterHealthcare Corp., Irvine, Calif., USA) was inserted into the trachea,with the balloon tip of the Fogarty catheter initially remaining in thetrachea. Volume-controlled ventilation was initiated at a respiratoryrate of 110-120 breaths per minute, at FiO₂ 1.0, a peak inspiratorypressure of 13 cm H2O, and a positive end-expiratory pressure level of2-3 cm H2O. A right parasternal thoracotomy was performed, and asmall-vessel ultrasonic flow probe (1RB; Transonic Instruments, Ithaca,N.Y.) was placed around the right pulmonary artery and fixed in positionusing a micromanipulator (X-tra Hand; TechniTool, Plymouth, Pa.). A 4-0silk suture was positioned around the left main pulmonary artery toallow transient vascular occlusion. A pulmonary artery catheter (PE10)was inserted into the main pulmonary artery by direct puncture. In otherexperiments, a lower thoracic aortic flow probe was placed as reportedpreviously (Steudel et al., supra).

In some studies, the pulmonary vein draining the right middle lobe waspunctured with a 30 G needle, connected to PE10 tubing, and secured witha microclip to assess left atrial pressure (PLA). To measure the partialpressure of oxygen in the aorta (PaO₂), a flexible polarographicClark-type PO₂ electrode (LICOX A3-Revoxode, 1.5 Fr.; GMS-Gesellschaftfuer medizinische Sondentechnik, Kiel, Germany), was advanced into theaortic arch -via the carotid artery. To measure the partial pressure ofoxygen in the pulmonary artery (PvO₂), the right ventricular outflowtract was punctured, and the oxygen electrode was advanced into thepulmonary artery. Electrodes were calibrated before and after eachexperiment in air at ambient pressure using a test probe barrel.Anesthesia was maintained with intraperitoneal ketamine (0.1 mg/g bw)and xylazine (0.01 mg/g bw) injections with intraperitoneal pancuronium(0.002 mg/g bw) added to produce muscle relaxation.

Bloodflow and pressure measurements. Mean systemic arterial pressure(PSA), mean pulmonary artery pressure (PPA), and in some studies PLA,were continuously monitored using biomedical amplifiers (Hewlett Packard8805C, Palo Alto, Calif.; Siemens Sirecust 960, Danvers, Mass.). Meanlower thoracic aortic flow (QLTAF) and right pulmonary artery flow(QRPA) were measured with small vessel flow probes connected to aflowmeter (T106; Transonic Instruments). In some experiments, leftventricular end-diastolic pressure was measured with a 1.4 Fr. Millarcatheter. The catheter was advanced through the right carotid arteryinto the left ventricle. All measured signals were transferred to ananalog-to-digital converter, displayed on a computer screen, andrecorded at 640 Hz using a data acquisition system (DI 220; DataqInstruments, Akron,Ohio) on a personal computer. All monitoringequipment was calibrated before each experiment.

Differential measurement of left and right pulmonary artery flow. Toassess the contribution of QRPA and left pulmonary artery flow (QLPA) tototal pulmonary artery flow (QPA), transient occlusion (90 seconds) ofthe left pulmonary artery (QLPA) was performed. QRPA during acute leftpulmonary artery occlusion was considered to be QPA (i.e., cardiacoutput) and correlated closely (r2=0.88; y=0.95x+0.38; n=9) with QLTAF.QLPA was calculated as the difference between QRPA during left pulmonaryartery occlusion (QPA) and QRPA with a patent left pulmonary artery(QLPA=QPA−QRPA). Absolute values of respective flows were recorded, andthe fractional distribution of flow to the right and left lungs(QRPA/QPA and QLPA/QPA) was calculated.

QPA was assessed by measurement of QRPA during transient occlusion ofthe left pulmonary artery (QLPA) because blood flow is lost to the upperextremities and the head when measured at the lower thoracic aorta.Moreover, adding a second flow probe increases the likelihood of error,because of the small size of the mouse, and increases surgical traumaand stress to the animal.

Unilateral alveolar hypoxia. To induce regional (i.e., left lung)alveolar hypoxia, the left mainstem bronchus was reversibly occluded(LMBO) by advancing a Fogarty catheter into the left mainstem bronchusand inflating the balloon tip under visual control. Complete collapse ofthe left lung was visually observed within about a minute and confirmedby transient overinflation of the right lung. PPA, PSA, and QRPA werecontinuously measured during LMBO. In some experiments, the collapsedleft lung was reinflated with 5% CO₂ in N2 to a peak airway pressure of30 cm H2O. QLPA was measured before and 5 minutes after LMBO.

Infusion of angiotensin II. Increasing doses of angiotensin II (0.05,0.5, and 5.0 ng/g bw per minute) dissolved in sterile normal saline wereinfused via the central venous catheter using an infusion pump (Pump 11;Harvard Apparatus Co., South Natick, Mass.). PLA, PPA, PSA, and QLTAFwere continuously measured.

Breathing with supplemental NO. Mice were housed in speciallyconstructed chambers (Steudel et al., supra) where they breathedspontaneously for 22 hours at an inspired oxygen fraction (FiO₂) of 0.21with 40 ppm NO added to the inspiratory gas mixture. After exposure,mice were removed from the chambers and breathed air during theinduction of anesthesia. Hemodynamic measurements were obtained 60minutes after removal from the chambers. During measurements, animalswere mechanically ventilated at FiO₂ 1.0 without supplemental NO.

Validation of pulmonary blood flow measurements. In saline-treatedwild-type mice (n=5), we compared simultaneous measurements offractional pulmonary blood flow distribution made using intravenousinjections of fluorescent-labeled microspheres (Glenny et al., 1993, J.Appl. Physiol. 74:2585-2597) with those made using ultrasonic flowprobes, as already described here. Before LMBO, 50,000 coloredmicrospheres (15-μm NuFlow Spheres; Interactive Medical TechnologiesLtd., West Los Angeles, Cailf.), suspended in 0.2 mL saline containing0.05% Tween-80 surfactant to prevent aggregation, were vortexed and thenimmediately infused (over 30 seconds) through a jugular vein cannula.After completion of the injection, the catheter was flushed with 0.1 mLsaline. After 5 minutes of LMBO, microsphere injection was repeatedusing microspheres of a different color. Animals were sacrificed, andthe lungs were harvested and weighed separately. Tissue samples wereanalyzed for total microsphere counts using flow cytometric analysis.The fraction of pulmonary blood flow to the right or left lung wascalculated as total spheres to right or left lung over total spheres inboth lungs.

In additional saline-treated wild-type mice (n=6), to confirm that theLMBO-induced redistribution of pulmonary blood flow was reflected by anincrease in left pulmonary vascular resistance, we directly measuredQLPA during transient occlusion of the inferior vena cava and calculatedthe slope and intercept of the left pulmonary artery pressure-flowrelationship.

Lung wet/dry ratio. After euthanasia with pentobarbital (0.1 mg/gintraperitoneally), both lungs, excluding hilar structures, wereexcised, blotted, and immediately weighed. Thereafter, the tissue wasdried in a microwave oven for 60 minutes, as described previously (20),and reweighed. Lung wet/dry ratio was calculated.

Statistical analysis. Changes of pulmonary blood flow are expressed asthe percent reduction of baseline blood flow. Differences between groupswere determined using a 2-way ANOVA. When significant differences weredetected by ANOVA, a post hoc Fisher's test was used (Statistica forWindows; StatSoft Inc., Tulsa, Okla.). A P value of less than 0.05indicated a significant difference. All data are expressed as mean±SEM.

Results

Effects of unilateral alveolar hypoxia on pulmonary blood flow. Toassess HPV in vivo, we developed a murine model in which differentialpulmonary blood flow measurements could be obtained before and duringleft lung unilateral alveolar hypoxia (FIGS. 9A-9C). Because occlusionof the right mainstem bronchus caused severe hypoxemia and hemodynamicinstability, we elected to occlude the left mainstem bronchus (LMBO),which produced a stable model of unilateral lung collapse. Differentialpulmonary blood flow was measured at thoracotomy using an ultrasonicflow probe placed around the right pulmonary artery, and the flowdistribution between the right and left lung was assessed by transientlyoccluding the left pulmonary artery (FIGS. 9A-9C).

FIGS. 9A-9C show representative tracings of pulmonary and systemichemodynamic measurements before (FIG. 9A), at the initiation of LMBO(FIG. 9B), and 5 minutes after LMBO (FIG. 9C) with and without transientleft pulmonary artery (LPA) occlusion. Transient occlusion of leftpulmonary artery flow did not produce any systemic hemodynamic effect(FIG. 9A). Total lung collapse occurred about 1 minute after LMBO.

Online recordings of mean flow through the right pulmonary artery(Q_(RPA)), mean pulmonary artery pressure (P_(PA)), mean systemicarterial pressure (P_(SA)), and mean airway pressure (P_(ALV)) in asaline-treated wild-type mouse at baseline and after LMBO are presented.To assess blood flow distribution between right and left pulmonaryarteries, the left pulmonary artery was transiently occluded, at whichpoint Q_(RPA)=Q_(PA) (see FIG. 9A and FIG. 9C). The difference of Q_(PA)and Q_(RPA) equals Q_(LPA.) Measurements were taken at baseline and 5minutes after LMBO. Arrows indicate occlusion (90 seconds) and releaseof left pulmonary artery. These representative tracings highlight theability to measure pulmonary blood flow distribution in vivo in themouse.

FIGS. 10A-10C show the experimental approaches used to validate themethod of measuring pulmonary blood flow distribution in the mouse. FIG.10A shows the correlation of percent pulmonary blood flow to the left orright lung assessed by intravenous injection of fluorescent microspheres(15 μm in diameter) and by simultaneous measurement of Q_(RPA) with anultrasonic flow probe. In the latter method, differential blood flowdistribution between the right and left pulmonary artery was assessed bytransient occlusion of the left pulmonary artery. Values are expressedas the fractional flow to the right or left lung before and after LMBO(saline-treated wild-type mice; n=4). Note the close agreement betweenthe 2 methods (r²=0.967). FIG. 10B shows results of experiments on theleft lung pulmonary flow-pressure relationship before (baseline) andafter 5 minutes of LMBO in saline-treated wild-type mice (n=6). Note thesignificant increase of the slope, which represents an increasedincremental left lung pulmonary vascular resistance induced by LMBO. Inthese studies, left pulmonary artery flow (Q_(LPA)) was measureddirectly using an ultrasonic flow probe, and the slopes were generatedby reducing Q_(PA) with a transient occlusion of the inferior vena cava(P<0.05, slope differs versus baseline). FIG. 10C illustrates changes intotal left lung pulmonary vascular resistance (TLPVR) duringre-expansion of the collapsed left lung in saline-treated wild-type mice(n=3). The left lung was inflated by a continuous injection of 5% CO₂ inN₂ up to a peak inspiratory pressure of 30 cm H₂O. Values are expressedas a linear regression of all data points with the respective 95%confidence intervals. These results demonstrated that the redistributionof pulmonary blood flow after LMBO is attributable to hypoxia and not toleft lung collapse.

Before LMBO, hemodynamic parameters did not differ between wild-typemice and NOS2-deficient mice. Five minutes after LMBO, QLPA/QPA wasreduced by 46±5% in saline-treated wild-type mice and by 50±7% insaline-treated NOS2-deficient mice (FIG. 7). In supplemental studies inwhich QLPA was measured directly using a flow probe around the leftpulmonary artery, we observed that the LMBO-induced pulmonary blood flowredistribution was reflected by an increase in incremental leftpulmonary vascular resistance from 102±18 mmHg•min•g•mL⁻¹ to 210±38mmHg•min•g•mL⁻¹ (FIG. 10B). LMBO-induced pulmonary blood flowredistribution was not attributable to mechanical factors associatedwith left lung collapse, as left pulmonary vascular resistance (LPVR)did not change when the collapsed lung was reinflated to a normal lungvolume under direct vision with 5% CO₂ in N2 (n=3; FIG. 10C).

Effect of endotoxemia on pulmonary and systemic hemodynamics duringunilateral alveolar hypoxia. After challenge with intraperitonealinjection of 10 mg/kg E. coli endotoxin, mice appeared lethargic withpiloerection and diarrhea. Approximately 50% of mice died within 1 weekafter endotoxin challenge, and there were no differences in mortalitybetween wild-type and NOS2-deficient mice (data not shown). Before LMBO,hemodynamic parameters did not differ between saline-treated mice andendotoxin-treated mice (FIG. 12), but QPA tended to be higher inendotoxin-treated wild-type mice than in NOS2-deficient mice (230±35 vs.120±32 μL•min⁻¹•g⁻¹ bw), although this difference did not reachstatistical significance. Comparison of QPA for all studiedendotoxin-challenged wild-type and NOS2-deficient mice confirmed thatthere was no difference between the two genotypes (wild-type mice 180±20μL/min per gram; NOS2-deficient mice 140±15 μl/min per gram; n=21 and15, respectively). Because differences in QPA potentially affectpulmonary blood flow redistribution, we tested whether changes inQLPA/QPA depended on changes in QPA. Linear regression analysis revealedno correlation between QPA and QLPA/QPA during LMBO (r2=0.03, both forall mice and for all endotoxin-treated mice (P<0.001; FIG. 7). AfterLMBO, the QLPA/QPA was reduced by 46±5% in saline treated wild typemice, and by 18±5% in endotoxin treated wild type mice. In contrast,LMBO reduced QLPA/QPA by 50±7% in saline-treated NOS2-deficient mice andby 51±6% in endotoxin-treated NOS2-deficient mice (FIG. 7). There was nodifference in the response to endotoxin between SV129, SV129B6F1, orC57BL/6 wild-type strains or between NOS2-deficient mice withSV129/B6F1-hybrid background and NOS2-deficient mice backcrossed for 10generations on a C57BL/6 background (data not shown).

Effect of endotoxemia on PaO₂ and PvO₂ during unilateral alveolarhypoxia. To determine whether the differences in LMBO-induced pulmonaryblood flow redistribution noted in wild-type and NOS2-deficient miceafter endotoxin challenge are reflected by differences in LMBO-inducedchanges in arterial oxygenation, the PaO₂ was continuously measuredbefore and during LMBO. In separate endotoxin-treated wild-type andNOS2-deficient mice, the effect of LMBO on PvO₂ was also assessed. Insaline-treated wild-type mice (n=4), breathing at FiO₂ 1.0, LMBO for 5minutes decreased the PaO₂ from 432±7 mmHg to 225±13 mmHg. The PaO₂ was342±23 mmHg in endotoxin-treated wild-type mice and 347±33 mmHg inendotoxin-treated NOS2-deficient mice. After 5 minutes of LMBO, the PaO₂decreased more in endotoxin-treated wild-type mice (145±9 mmHg) than inendotoxin-treated NOS2-deficient mice (230±18 mmHg; P<0.05; FIG. 11).

PvO₂ did not differ in endotoxin-treated wild-type mice andendotoxin-treated NOS2-deficient mice (before LMBO: 39±5 and 44±8 mmHg,respectively; after LMBO: 34±4 and 43±7 mmHg, respectively; n=3 for bothgroups).

Prolonged Pharmacologic Inhibition of NOS2 Activity. To determinewhether prolonged pharmacologic inhibition of NOS2 preserves HPV,wild-type mice (n=5) were injected intraperitoneally with 10 mg/kgendotoxin, and 3 hours later were treated with L-NIL (5 mg/kgintraperitoneally), a selective inhibitor of NOS2 activity. This dose ofL-NIL was sufficient to prevent the increase in pulmonary cGMP levels inwild-type mice 7 hours after endotoxin challenge (data not shown).Pulmonary blood flow studies were performed 22 hours after the endotoxinchallenge. In endotoxin-exposed mice treated with L-NIL, we measured nodifferences in systemic and pulmonary hemodynamics before LMBO, comparedwith saline-treated or endotoxin-treated wild-type mice. The reductionof QLPA/QPA was greater in endotoxin-challenged wild-type mice treatedwith L-NIL than in wild-type mice receiving endotoxin alone (53±10% vs.18±5%, respectively; P<0.01; FIG. 7).

Acute pharmacologic inhibition of NOS2 with L-NIL. To determine whetheracute inhibition of NOS2 enzyme activity augmented HPV during LMBO,pulmonary blood flow studies were performed in saline-treated andendotoxin-treated wild-type mice during which L-NIL (5 mg/kgintravenously) was administered after LMBO. In saline-treated wild-typemice (n=5), acute L-NIL administration did not further reduce QLPA/QPAduring LMBO (49±3% before L-NIL; 56±3% after L-NIL). All otherhemodynamic parameters did not change after L-NIL injection. Inwild-type mice treated with endotoxin 22 hours earlier (n=4), acuteL-NIL administration did not further reduce QLPA/QPA during LMBO (22±11%reduction before L-NIL; 24±18% reduction after L-NIL).

Prolonged inhalation of 4 or 40 ppm NO. To learn whether increasedpulmonary levels of NO, rather than another NOS2 product, contribute tothe endotoxin-induced impairment of HPV, saline-treated andendotoxin-challenged wild-type and NOS2-deficient mice breathed 40 ppmNO in air for 22 hours. The hemodynamic studies were performed 1 hourlater, allowing ample time for any potential vasodilator action ofinhaled NO to dissipate. Inhalation of 40 ppm NO for 22 hours did notimpair HPV in saline-treated wild-type mice and NOS2-deficient mice:reduction of QLPA/QPA after LMBO was 51±10% in saline-treated wild-typemice and 50±11% in saline-treated NOS2-deficient mice after breathing 40ppm NO for 22 hours (FIG. 7). Except for a modest difference in heartrate, no other differences in pre-LMBO hemodynamics were found betweenendotoxin-treated and saline-treated mice exposed to prolongedinhalation of 40 ppm NO for 22 hours (FIG. 12). After prolongedinhalation of 40 ppm NO, endotoxin-treated NOS2-deficient micedemonstrated a marked attenuation of HPV compared with endotoxin-treatedNOS2-deficient mice that did not breathe supplemental NO (reduction ofQLPA/QPA: 20±7% vs. 50±11%, respectively; P<0.05; FIG. 7). In contrast,prolonged NO inhalation did not affect the endotoxin-induced impairmentof HPV in wild-type mice (reduction of QLPA/QPA: 19±10% inendotoxin-treated wild-type mice breathing 40 ppm NO for 22 hours versus18±5% in endotoxin-treated wild-type mice not exposed to NO; FIG. 7). Incontrast, breathing 4 ppm NO for 22 hours did not impair HPV inendotoxin-treated NOS2-deficient mice (reduction of QLPA/QPA: 62±2%;n=4).

Pulmonary vasoreactivity to angiotensin II. To determine whether theimpact of endotoxin on HPV was attributable to a nonspecific effect ofendotoxin on pulmonary vascular contractile function, we measured thepulmonary vasoconstrictor response to increasing intravenous doses ofangiotensin II in saline-treated wild-type mice and wild-type mice 22hours after endotoxin challenge. PVR increased from 74±24 at baseline to184±25 mmHg•min•g•mL-1 at 5.0 μg/kg per minute angiotensin II insaline-treated wild-type mice without endotoxin (P<0.01) and from 55±11to 174±40 mmHg•min•g•mL⁻¹ in endotoxin-challenged wild-type mice(P<0.001). At any angiotensin II infusion dose level, there was nodifference in the PVR of endotoxin-treated and saline-treated mice. PLAat baseline did not differ between saline-treated wild-type mice (6±1mmHg) and endotoxin-treated wild-type mice (5±1 mmHg), and PLA did notchange in response to angiotensin II infusion in either group.

Lung wet/dry weight ratios. Wet/dry lung weight ratios did not differbetween endotoxin-challenged wild-type (wet weight/dry weight: 5.0±0.5)and NOS2-deficient mice (4.6±0.2), or saline-treated wild-type (4.6±0.1)and saline-treated NOS2-deficient mice (4.5±0.1). Breathing 4 or 40 ppmNO for 22 hours did not alter the wet/dry lung weight ratios.

Summary and Interpretation of Experiments. To investigate the role of NOand NOS2 in the impairment of HPV in sepsis, we developed an in vivomouse model to assess the redistribution of pulmonary blood flow inresponse to unilateral alveolar hypoxia produced by LMBO. In mice notexposed to endotoxin, LMBO doubled left lung PVR, thereby diverting 50%of left pulmonary blood flow to the right lung and causing a modestdecrease in PaO₂. Changes in murine pulmonary blood flow distributionmeasured using ultrasonic flow probes at thoracotomy were closelycorrelated with measurements obtained using intravenous injection offluorescent microspheres (see FIG. 10A) and were similar to thosereported by investigators studying large animal models (Domino et al.,1984, Anesthesiology 60:562-566; Sprague et al., 1992, Proc. Natl. Acad.Sci. USA 89:8711-8715.

In wild-type mice 22 hours after an endotoxin challenge, we observedthat the ability to redistribute pulmonary blood flow in response toregional lung hypoxia was severely impaired, leading to a markeddeterioration in systemic arterial oxygenation. This endotoxin-inducedimpairment of pulmonary blood flow redistribution in the mouse issimilar to that observed in awake sheep after intravenous challenge withlive bacteria (Fischer, et al., 1997, Am. J. Respir. Crit. Care Med.156:833-839) or endotoxin (Hutchison et al., 1985, J. Appl. Physiol.58:1463-1468).

It did not appear that the endotoxin-induced impairment of HPV was dueto nonspecific dysfunction of the vasomotor contractile apparatusbecause we found that the ability of angiotensin II to vasoconstrict thepulmonary vasculature did not differ in endotoxin-challenged andsaline-treated mice. Moreover, the deleterious effect of endotoxin onthe murine pulmonary vasculature was reversible with restoration of HPVat 14 days after endotoxin administration (data not shown).

In NOS2-deficient mice challenged with endotoxin 22 hours earlier, HPVwas not impaired and there was preservation of systemic arterialoxygenation during LMBO. Similarly, HPV was preserved in wild-type micetreated with L-NIL, a specific inhibitor of NOS2 enzyme activity, 3hours after endotoxin challenge. These results demonstrate that NOS2enzyme activity is critical to produce the endotoxin-induced impairmentof HPV.

It is unlikely that impairment of HPV in wild-type mice 22 hours afterendotoxin challenge is attributable to excess pulmonary NO levels, asacute administration of L-NIL immediately after LMBO did not restoreHPV. These results demonstrate that endotoxin-induced pulmonary NOS2expression is necessary to impair HPV but that continued NOS2 activityis not required for the impairment of HPV measured 22 hours after theendotoxin challenge.

Under certain conditions, NOS2 can produce superoxide, as well as NO(28). We examined whether NO produced by NOS2 contributed to theendotoxin-induced impairment of HPV by replenishing pulmonary NO levelsvia inhalation in endotoxin-challenged NOS2-deficient mice.NOS2-deficient mice were challenged with endotoxin and placed in anexposure chamber containing varying concentrations of NO for 22 hours.Pulmonary blood flow redistribution in response to LMBO was measured 1hour after removal from the chamber, by which time pulmonary NO levelswould not be expected to be elevated. HPV was impaired inendotoxin-challenged NOS2-deficient mice that breathed 40 ppm NO (seeFIG. 7). In contrast, breathing 4 ppm NO for 22 hours did not impair HPVin endotoxin-treated NOS2-deficient mice. These data suggest thatmarkedly elevated pulmonary NO levels (either produced endogenously byNOS2 or inhaled) are required to impair HPV. If our observations in miceare extrapolated to human beings, an important clinical implication ofour studies is that the administration of high concentrations of inhaledNO to patients with pulmonary inflammation may attenuate HPV, leading toa paradoxical decrease in arterial oxygenation. Moreover, these findingssupport the current clinical practice of using the lowest effectiveconcentration of inhaled NO when treating patients with acuterespiratory failure (Zapol, 1993, Intensive Care Med. 19:433-434).

In saline-treated wild-type and NOS2-deficient mice, inhalation of 40ppm NO for 22 hours did not impair HPV when the animals were studied 1hour after removal from the exposure chamber (see FIG. 7). These resultssuggest that sustained increases in pulmonary NO levels alone areinsufficient to cause lasting impairment of HPV. In addition, breathing40 ppm NO for 22 hours did not further impair HPV inendotoxin-challenged wild-type mice. Thus, it appears that inhaled NOand endotoxin-induced pulmonary NO production are not additive withrespect to impairing HPV. Our studies suggest that the lastingimpairment of HPV after endotoxin challenge requires both increasedpulmonary NO levels and additional endotoxin-induced inflammatoryproducts.

EXAMPLE 3 Leukotriene Blockers and Impairment of HPV

Experimental evidence was obtained demonstrating that inhibitors ofleukotriene synthesis and inhibitors of leukotriene receptor activationprevent the impairment of HPV in endotoxin-challenged mice. We foundthat HPV is preserved in endotoxin-challenged mice deficient in5-lipoxygenase (5LO), which catalyzes conversion of arachidonic acidinto leukotriene A4, when 5LO-activating protein (FLAP) is present. Wefound that in wild-type mice, HPV is preserved in endotoxin-challengedmice treated with FLAP inhibitor MK886, or CysT1 receptor blocker MK571.For these experiments, we used an in vivo mouse model of one-lunghypoxia.

Wild-type (SV129B6/F1) mice and 5LO-deficient mice were anesthetized andstudied at thoracotomy. Left pulmonary artery flow (QLPA) and pulmonary(PPA) and systemic (PSA) artery pressures were measured continuously.Pressure flow relationships for the left pulmonary circulation wereobtained by transient occlusion of the inferior vena cava.

HPV was assessed as the percent increase in left pulmonary vascularresistance (the slope of the P/Q-relationship, LPVR) after left mainbronchus occlusion (LMBO). LMBO increased LPVR by 99±13% in 5LOdeficient mice, and by 100±11% in wild-type mice. Data are summarized inFIG. 13. These results demonstrated that inhibition ofcysteinyl-leukotriene synthesis or receptor activation prevented theendotoxin-induced impairment of HPV.

OTHER EMBODIMENTS

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the invention can be practiced using anti-ROS agents andleukotriene blockers other than the ones listed herein. Accordingly,other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method for reducing, partially preventing orcompletely preventing nitric oxide inhalation-related impairment ofhypoxic pulmonary vasoconstriction in a mammal, comprising:administering to the mammal a therapeutically effective amount of nitricoxide by inhalation, and co-administering an amount of at least oneanti-reactive oxygen species (anti-ROS) agent effective to reduce,partially prevent or completely prevent nitric oxide inhalation-relatedimpairment of hypoxic pulmonary vasoconstriction in the mammal.
 2. Themethod of claim 1, wherein the anti-ROS agent is selected from the groupconsisting of: allopurinol, bilirubin, caffeic acid, catalase,PEG-catalase, catechin, ceruloplasm, copper diisopropylsalicylate,deferoxamine mesylate, dimethylurea, ebselen, EUK-8, FeTMTPyP, FETPPS,glutathione, MnTBAP, MnTMPyP, selenomethionine, superoxide dismutase,PEG-superoxide dismutase, and dihydroquercetin.
 3. The method of claim1, wherein the anti-ROS agent is N-acetylcysteine.
 4. The method ofclaim 1, further comprising co-administering an effective amount of aleukotriene blocker. 5.The method of claim 4, wherein the leukotrieneblocker is prankulast, MK-571, MK-591, MK-886, BAYx1005, cinalukast,pobilukast edamine, MK-679, or ZD2138.
 6. The method of claim 4, whereinthe leukotriene blocker is montelukast, zafirlukast.
 7. The method ofclaim 1, wherein the mammal has acute pulmonary injury.
 8. The method ofclaim 1, wherein the mammal has acute respiratory distress syndrome. 9.The method of claim 1, wherein the mammal has diffuse pulmonaryinfection.
 10. The method of claim 1, wherein the mammal has sepsis. 11.The method of claim 1, wherein the mammal has lung inflammation.
 12. Themethod of claim 1, wherein the method comprises co-administering to themammal two or more-different anti-ROS agents.
 13. The method of claim 1,wherein the anti-ROS agent is administered to the mammal by inhalation.14. The method of claim 1, wherein the anti-ROS agent is administered tothe mammal by intravenous administration.
 15. The method of claim 1,wherein the administration of the anti-ROS agent is commencedconcurrently with initiation of nitric oxide inhalation.
 16. The methodof claim 1, wherein the anti-ROS agent is a scavenger of peroxynitrite.17. The method of claim 1, wherein the anti-ROS agent is aglucocorticod.
 18. The method of claim 1, wherein the anti-ROS agent isascorbic acid (vitamin C) or vitamin E.
 19. A method for reducing,partially preventing or completely preventing loss of pulmonaryvasodilatory responsiveness to nitric oxide inhalation in a mammal,comprising: administering to the mammal a therapeutically effectiveamount of nitric oxide by inhalation, and co-administering an amount ofat least one anti-ROS agent effective to reduce, partially prevent orcompletely prevent loss of pulmonary vasodilatory responsiveness tonitric oxide inhalation in the mammal.
 20. The method of claim 19,wherein the anti-ROS agent is selected from the group consisting of:allopurinol, bilirubin, caffeic acid, catalase, PEG-catalase, catechin,ceruloplasm, copper diisopropylsalicylate, deferoxamine mesylate,dimethylurea, ebselen, EUK-8, FeTMTPyP, FETPPS, glutathione, MnTBAP,MnTMPyP, selenomethionine, superoxide dismutase, PEG-superoxidedismutase, and dihydroquercetin.
 21. The method of claim 19, wherein theanti-ROS agent is N-acetylcysteine.
 22. The method of claim 19, furthercomprising co-administering an effective amount of a leukotrieneblocker.
 23. The method of claim 22, wherein the leukotriene blocker isprankulast, MK-571, MK-591, MK-886, BAYx1005, cinalukast, pobilukastedamine, MK-679, or ZD2138.
 24. The method of claim wherein theleukotriene blocker is montelukast, zafirlukast, or zileuton.
 25. Themethod of claim 19, wherein the mammal has acute pulmonary injury. 26.The method of claim 19, wherein them acute respiratory distresssyndrome.
 27. The method of claim 19, wherein the mammal has diffusepulmonary infection.
 28. The method of claim 19, wherein the mammal hassepsis.
 29. The method of claim 19, herein the mammal has lunginflammation.
 30. The method of claim 19, wherein the method comprisesco-administering to the mammal two or more, different-anti ROS agents.31. The method of claim 19, wherein the anti-ROS agent is administeredto the mammal by inhalation.
 32. The method of claim 19, wherein theanti-ROS agent is administered to the mammal by intravenousadministration.
 33. The method of claim 19, wherein the administrationof the anti-ROS agent is commenced concurrently with initiation ofnitric oxide inhalation.
 34. The method of claim 19, wherein theanti-ROS agent is a scavenger of peroxynitrite.
 35. The method of claim19, wherein the anti-ROS agent is a glucocorticoid.
 36. The method ofclaim 19, wherein the anti-ROS agent is ascorbic acid (vitamin C) orvitamin E.